Spray coating



July 8, 1958 J. w. JUVINALL SPRAY COATING Original Filed Dec. 7, 1941 x m w m JAMES W. JUVINAL L BY W10 1 Attorney United States Patent O sPRAy COATING James W. Juvinall, Brendonwood, I nd., assignor to Ransburg Electra-Coating Corp., a corporation of Indiana Original application December 7, 1941, Serial No. 260,431, now Patent No. 2,724,661, dated November 22, 1955. Divided and this application August 3, 1955, Serial No. 526,096

16 Claims. '(Cl. 117-93) This invention is a division of copending application Serial No. 260,431, filed December 7, 1951, now Patent No. 2,724,661, and relates to electrostatic spray coating of articles by a method and apparatus wherein the coating material is atomized, dispersed and deposited upon the articles being coated; and in particular relates to the coating of those portions of articles which comprise adjacent divergent surfaces, as the flanged bottoms of certain articles, which portions are not readily satisfactorily coated by electrostatic coating methods heretobefore employed.

4 In the electrostatic coating of articles with which we are here concerned the particles are atomized from the head under the influence of an electrostatic field and are then dispersed in a certain pattern and eventually deposited on the article, normally maintained at a substantial potential differential from the head. Under normal conditions the article is substantially spaced from the atomizing head and accordingly, the angle intercepted by a small diverging surface, as aflange around the bottom of the article, is relatively small; and further a flange extending directly toward the atomizing head has its inner surface substantially parallel to the general line of movement of the spray particles at a substantial distance from the head, where they normally move substantiallyparallel to the axis of the head. These factors contribute to insutficient coating of the inner surfaceof a vertical flange, for example.

' The present invention provides methodand apparatus for satisfactorily coating this particular portion of an article; and, in conjunction with other coating methods and apparatus heretofore used, enables a coating of sub; stantial thickness to be applied to the entire surface of the article, including a flanged bottom portion, for example. Generally speaking, this is accomplished by cating the diverging surfaces (as a flanged container bottom) fairly close to a spray source so that the coating spray is relatively highly concentrated per unit area and has a general line of movement which is still diverging sharply'outwardly from the head (i., e., outwardly from the axis thereof); so that the field electrode cooperating with the divergingor flanged surface lies to the inside of and fairly close to the flange, with -a relatively large n'umber of lines of force'passing' to theinner flange surface; so that the projection of the diverging surface, as a vertical flange, subtends -a relativelygreater angle in the spray pattern, particularly as related to the general line or direction of spray movement; and so that ,the field, strength at the juncture line between the flange and the area from which it extends is large enough to cause a substantial deposition offthe coating material The present invention further provides apparatus andamethod whereby surfaces havingflanged borders (such for example as the bottom'surfaces of some containers) can be completely coated satisfactorily through the use of an electrostatic coating system-employing only atomizing heads which have proved particularly elficientcommercially. a I

Qneform of electrostatic-coating arrangement which proved very satisfactorycommercially makes use of 2,842,460 Patented July 8,

2 an atomizing head with a circular atomizing edge, as the, edge of a conical member maintained at a potential with respect to its surroundings, and rotates this edge while liquid coating material is supplied through anopening in the'apex thereof. The material flows in the form of a thin film along the interior of the cone of the edge thereof, is atomized from this edge, and under the effect of an electrostatic field having the head as one electrode passes to the article to be coated. The article is usually conducting and mounted on a grounded conveyor to comprise the other electrode. static atomizing head is more fully disclosed and claimed in the copending application of Edwin M. Ransburg,

Serial No. 143,994, filed February 13, 1950. The naturalpattern delivered from a head of this type normally is bell shaped in cross-section through the axis of the head, with the general line of movement of the spray initially diverging sharply outwardly from'the head andthen curving inwardly until ultimately, at a substantial distance from the atomizing head, it is substantially parallel to the axis thereof; and the pattern transverse to the axis is in the form of a doughnut or annular band having a central portion which is completely or relatively void of coating materiaL'a pattern band which has a more concentrated distribution of coating particles --near the center line thereof than near the edges. The natural pattern (sometimes hereinafter referred to as merely the pattern), to which reference is here being made, is thepattern which the spraying device would provide on a large flat sheet of'conducting material of relatively infinite size arranged normal to the general line of movement of the spray particles'and acting as the other field electrode. r i a Rotary heads providing an annular pattern of this type have proved particularly satisfactory in electrostatic coating'of large articles or large surfaces, particularly'whengrouped in sets of three in the manner more particularly.

described and claimed in my copending application. Serial No. 257,741, filed November 23, 1951. this type of atomizer which produces a bell-like cone of spray resulting in an annular spray pattern is used in heretofore normal manner, the side walls of recessed areas, as the-side walls of flanges and their junctionlin'e with the surface from which they diverge, will frequently be so lightly coatecl'relative to the remainder of the article as to be insufiiciently protected. The present invention,;

however, by using the methods and apparatus hereinafter more fully described in conjunction with other arrangements for coating other areas, results in a satisfactory coating ofthese portions while still retaining the coating efliciencies and convenience of such an electrostatic coat the necessity of over-coating other areas. s 1 t a r The foregoing and other features of this invention will be apparent from the following specification and the drawings inwhich: e

Figure l is a perspective view of one form of coating apparatus embodying this invention, illustrating the ap-' plication of coating material to the exterior surfaces of large cylindrical containers flanged bottoms; and

' Figure 2 is a diagrammatical view illustrating the spray pattern and its relation to the flanged portions while they are particularly being coated;

While one arrangement of coating systems is illus-' trated in the accompanying drawings and will be hereinafter more fully described, it will be understood that this is in all respects-a representative embodiment only.

It is to be understood that other embodiments of the method and apparatus here disclosed, Falone orin com bination withother coating arrangements, maybe utilized Without departing from the. contemplated scopeof Such a rotary conical type electro However, When;

(as five gallon cans) with the present invention, and that no limitations are to be implied from such specific description as is hereinafter set forth. 2

Referring now: more especially to the particular-embodiment of the invention illustrated in Figure 1, the articles to be coated (here illustrated as cylindrical cans or drums with flanged bottoms) are inverted over and carried by spindles 11 which are mounted for suitablyspaced traversing movement, as by being mounted on a chain 12 longitudinally movable in a channel member 13. The spindles are arranged to be rotated as they are traversed, the rotation being effected by virtue of engagement of spindle portions with a belt 14 passing over pulleys 15 and 16 in the particular form shown. The articles are thus traversed along the floor mounted conveyor as illustrated, and rotated suitably during such movement to increase the uniformity of distribution of coating.

Adjacent one side of the conveyor in the form here illustrated is a three-head atomizing arrangement for effecting the major portion of the coating operation, although it will-be understood that in practice a similar system might be used onthe opposite side of the conveyor to enable faster conveyor operation. The main coating arrangement illustrated comprises stands 17 and 18 from which rise vertical columns 19 and 20, in turn carrying between them an angularly arranged support member comprising the parts 21, 22, 23 and 24. These in turn carry three conical rotating atomizing heads here identified as 25, 26 and 27, adapted to be rotated through suitable drive connections by a motor 38. These heads are preferably of different diameters and suitably spaced to secure the optimum uniformity of distribution of coating material, as is more fully described and claimed in the above mentioned application of James W. Juvinall. The three heads are raised to a desired electrical potential, as by being connected together by having the support sections 22 and 23 of conducting material and by havinga cable connection 28 to one terminal of a high potential power pack 29, which may have its other terminal grounded as indicated at 30. These heads are also suitably supplied with liquid coating material, as by the hoses 31, 32 and 33 from a controlled :positive feed pump 34 drawing its liquid coating material from a container 35, forming a reservoir thereof. Since the articles are grounded, suitable field conditions.(as by having theheads spaced 12 inches from the nearest surface of the articles and at a voltage diiferentialof 100,000 volts with respect thereto) result in atomizing the coating material from the heads and depositing it upon the side walls of the, containers; and further causes a substantialcoating of the bottom of the container, at least as to allportions except those comprising the inner vertical surfaces of the flanges and the closely adjacent bottom areas, which comprise. a critical area that will not be satisfactorily coated by the three head arrangement illustrated at the sides of the articles without overcoating of other areas. i

In order to provide such adequate coating, the present invention contemplates the use of an additional head positioned above the article being coated thereby and in a particular relation thereto and of a diameter specifically related to the diameter of the bottom of the can, this additional head being illustrated'to the left of Figure 1. If this head were located and arranged similarly to the heads heretofore just described, it would have a tendency to provide a more general coating of the bottom and. accordingly, it is contemplated that specific locationsand relationships will be provided such as to satis f-actorily coat the adjacent diverging surfaces at and near the juncture line of the flanges with the large bottom area.

Referring now more particularly to Figure 2, it will beseenthat if a head 40 of 6 inch-diameter were arranged at about twelve inches from the article, as in conventional commercial practice, the flange 10a (as.

illustrated in dotted lines at the lower left of the figure) would extend over only a very small fraction of the total pattern, would lie in the portion of spray movement where the general line of movement is parallel to the axis of the head, and would thus receive an unsatisfactorily small portion ofthe spray particles. However, by using a head of a diameter substantially smaller than the spacing between flanges and locating the article closer to the head than the diameter of the head, and with the juncture line between the surface and the flange 10a at or near the center line of the pattern band (and preferably a little to the outside thereof), the inner surface of the flange will both subtend a greater angle with respect to the diverging spray particles, receive more field force lines, and lie in a relatively denser portion of the spray, and a portion where the general line of movement of the spray is still substantially outwardly. This is particularly true if the portions to be specially coated by this latter head are moved in or through the pattern band with the line of juncture between the diverging surfaces at or near the center of the annular band, preferably slightly outside thereof and parallel thereto (or parallel to a line tangent to such center line at any instant).

Referring now more particularly to Figure 1 again, it will be seen that the additional head 40 is supported by a suitable insulating shaft 41 from the vertical post 42 and adapted to be rotated by the motor 43. The head is connected through the cable 44 to the power pack 29 to be raised to a suitable potential with respect to ground and is supplied with liquid coating material from the pump 34 through the hose 45. In the particular example illustrated the head 40 rnight be so located as to be 4 /2 inches away from the closest portion of the article moving along the conveyor, and would be at a lesser potential differential from ground than the other heads, as 5 0,000 volts.

The vertical post or column 42, and thus the entire assembly carried by it, is mounted on a block 46 in turn mounted on ways or guide members'47, these in turn being supported in desired relation to the conveyor, as by stands 48. Two compression coil springs 49 are here shown as arranged about the ways 47 in such a manner as to bias the block 46 toward the right (as illustrated in Figure 1). A shaft 50 driven by and in synchronization with the conveyor chain 12 is here shown as having a worm 51 at the lower end thereof driving the worm gear 52 on the shaft 53. This is here shown as driving through sprockets 54 and 55, chain 56 and a reduction gear arrangement 57, a cam here identified as 58 coopcrating with a follower pin 59011 the block 46.

Movement of conveyor chain 12 to the left causes rotation of the cam 58in a counterclockwise direction (as the parts are viewed in Figure 1), and this in turn causes traversing movement of the head 40 in synchronization with such movement of the particular article 10 being coated, so as to maintain the head and article in the relationship illustrated in Figure 2 for a substantial period. During this period the article is rotated about its own center with the center of rotation substantially coinciding with the center of the annular pattern being delivered by the conical atomizing head. After this desired relationship has been maintained for a sufiicient period, the cam will have reached the position illustrated in Figure l, whereupon the head 40 and its supporting arrangement will have moved back toward their farthest right hand position as viewed in the drawing, and will shortly thereafter start movement in synchronized relationship with the next article. During this traversing movement of the head relative to the article bottom, there will be a furtherc'oating of the central portions of the bottom surface by the head 40 supplementing the coating previous,

'ly received from the other atomizing heads. 7 9

As will be apparent from the foregoing description,

the correct choice of the sizeof the head-and its spacing is important in order that the field relationships and the size of the pattern be correctly related with the particular spaced portions to be coated. It is further to be seen that the use of a relatively close spacing of the head from the work, preferably a spacing less than the head diameter, enables a concentrated spray pattern; and the location of the diverging flange surface near, but preferably to the outside of the center line of the spray pattern provides a desired angular relationship for increasing the coating thickness. The operating voltages must, of course, be correctly chosen to stay below those which would cause sparking or arcing at the head spacings used. It is seen therefore that the invention resides not only in moving the spaced portions being coated through opposite sides of the annular spray pattern band but also in the correct correlation of head size, head spacing and operating voltage relative to the article surface being coated. Further the utilization of suitable spacings and head diameters, relative to the distance between the flange portions, is of importance in having the spray particles travel outwardly rather than straight toward the article as they approach the flanges, insuring better coating of the inner surfaces of vertical flanges.

While I have shown and described certain embodiments of my invention, it is to be understood that it is capable of many modifications. Changes, therefore, in the construction and arrangement may be made without departing from the spirit and scope of the invention as disclosed in the appended claims.

I claim:

1. Apparatus for electrostatically coating a pair of spaced portions of an article wherein each of said portions comprises adjacent divergent surfaces, comprising; an atomizing head for providing a spray of coating material in a pattern which is an annular band; means providing an electrostatic field from said head to said spaced portions being coated; and means for rotating said article during such coating with the center of rotation being substantially midway between said spaced portions and substantially coinciding with the center of said annular band for a substantial period of time, with the atomizing head diameter and the spacing of the head from the article both being less than the spacing between said spaced divergent portions.

2. Apparatus for electrostatically coating the edge portion of a generally circular surface of an article with a flange extending around and diverging from the edge thereof, comprising: an atomizing head for providing a spray of coating material in a pattern which is an annular band; means providing an electrostatic field from said head to the edge portion being coated; and means for rotating said article with the center of rotation sub-' stantially coinciding with the center of said surface and the center of said annular band for a substantial period of time, with the juncture line between said surface and flange being at or near the center line of said annular band.

3. Apparatus of the character claimed in claim 2,

wherein said article is carried by a conveyor and traversed during such rotation, and said atomizing head is carried by traversing means synchronized with conveyor movement.

4. Apparatus of the character claimed in claim 1, wherein said article is carried by a conveyor and traversed during such rotation, and said atomizing head is carried by traversing means synchronized with conveyor movement.

5. A method for electrostatically coating a pair of spaced portions of an article wherein each of said portions comprises adjacent divergent surfaces, comprising: providing from an atomizing head a spray of coating material in a pattern which is an annular band; providing an electrostatic field from said head to said spaced portions being coated; and rotating said article during such coating with the center of rotation being substantially midway between said "spaced portions and substantially coinciding with the center of said annular band for a substantial period of time so that said spaced portions move in opposite sides of said annular band;

6. A method for electrostatically coating spaced portions of an article having a surface of substantial size with relatively small flange portions diverging from opposite sides thereof, comprising: providing from a singlefluid atomizing head a spray of coating mat rial in a pattern which is an annular band; providing an electrostatic field from said head to said spaced portions being coated, said electrostatic field having a strength capable of effecting electrostatic atomization; rotating and traversing said article during such coating so that said spaced portions move through opposite sides of said annular band, the diameter of the head and its spacing from the article both being less than the spacing between flanges; and traversing said head with said article for at least a part of its movement.

7. Apparatus for.electrostatically coating an article, comprising: a first atomizing head in electrostatic coating relationship with said article; and a second atomizing head in-electrostatic coating relationship with a critical portion of said article, the spacing of said second head and its potential both being substantially less than those of the first head.

8. Apparatus for electrostatically coating an article, comprising: a first atomizing head in electrostatic coating relationship with said article; a second atomizing head in electrostatic coating relationship with a critical portion of said article, the spacing of said second head and the potential difference between it and the article both being substantially less than those of the first head; means for traversing said article during the coating operation; and means for traversing said second head in synchronism with the article during at least a portion of the coating.

9. A method for electrostatically coating an article, comprising: providing a spray of coating material from a first atomizing head; providing a spray of coating material from a second atomizing head; traversing said article in a path bringing it into coating relationship with each of said heads and closer to said second head than said first head; and providing a substantially greater potential between said article and said first head than between said article and said second head.

10. A method for electrostatically coating an article, comprising: providing a spray of coating material from a first atomizing head; providing a spray of coating material from a second atomizing head; traversing said article in a path bringing it into coating relationship with each of said heads and closer to said second head than said first head; providing a substantially greater potential difierence between said article and said first head than between said article and said second head; and maintaining a portion of said article in coating relationship with said second head substantially longer than with said first head.

11. Apparatus for electrostatically coating a generally circular surface of an article with a flange extending around and diverging from the edge thereof, comprising: an atomizing head for providing a spray of coating material in a pattern which is an annular band; means providing an electrostatic field from said head to the article being coated; means for rotating said article with the center of rotation substantially coinciding with the center of the surface and the center of said annular band for a substantial period of time, with the juncture line between said surface and flange being substantially at the center line of said annular band, to coat the edge portion of the article; and means for traversing the article with respect to the head, through at least a portion of said annular band to coat the center portion of said circular surface.

12. Apparatus of the character described in claim 11,

7 wherein said article passes into and out of said annula band with a traversing movement.

13. A method for electrostatically coating an article having portions comprising adjacent divergent surfaces and an intermediate portion, comprising: providing from an atomizing head a spray of coating material in a pattern which is an annular band; providing an electrostatic field from said head to the portions being coated; rotating said article during such coating with the center of rotation being substantially midway between said spaced portions and substantially coinciding with the center of said annular band for a substantial period of time so that said spaced portions move in opposite sides of said annular band; and traversing said article through at least a portion of said annular band to coat the intermediate portion thereof.

14. The method of claim 13, wherein said article is traversed into and out of said annular band.

15. Apparatus for electrostatically coating an article comprising: a first atomizing head in coating relationship with said article; a second atomizing head in coating relationship with said article, one of said heads being in coating relationship with a critical portion of the article; a source of electrostatic potential; means connecting said first head with said source of electrostatic potential, ap-

plying a potential thereto for effecting electrostatic coating of material on said article; and means connecting said second head with said source of electrostatic potential, applying a potential thereto for effecting electrostatic coacting of material on said article, the potential applied to said second head being substantially less than that applied to said first head.

16. A method for electrostatically coating an article comprising: providing a spray of coating material from a first atomizing head; providing a spray of coating material from a second atomizing head; traversing said article in a path bringing it into coating relationship with each of said heads, said path bringing a critical porton of said article into coating relationship with one of said heads; providing a potential between said article and said first head; and providing a potential between said article and said second head, the potential between the article and first head being greater than the potential between the article and second head.

Ransburg May 30, 1950 Crouse Sept. 18, 1951 

5. A METHOD FOR ELECTROSTATICALLY COATING A PAIR OF SPACED PORTIONS OF AN ARTICLE WHEREIN EACH OF SAID PORTIONS COMPRISES ADJACENT DIVERGENT SURFACES, COMPRISINGS: PROVIDING FROM AN ATOMIZING HEAD A SPRAY OF COATING MATERIAL IN A PATTERN WHICH IS AN ANNULAR BAND, PROVIDING AN ELECTROSTATIC FIELD FROM SAID HEAD TO SAID SPACED PORTIONS BEING COATED, AND ROTATING SAID ARTICLE DURING SUCH COATING WITH THE CENTER OF ROTATION BEING SUBSTANTIALLY MIDWAY BETWEEN SAID SPACED PORTIONS AND SUBSTANTIALLY COINCIDING WITH THE CENTER OF SAID ANNULAR BAND FOR A SUBSTANTIAL PERIOD OF TIME SO THAT SAID SPACED PORTIONS MOVE IN OPPOSITE SIDES OF SAID ANNULAR BAND. 